parallel build fixes for 7.4.2

[Simon Marlow]

On 24/02/2012 08:16, Conrad Parker wrote:
> Hi,
>
> recently we've been tweaking our internal build system at Tsuru to
> handle parallel builds of both cabal packages via 'cabal-sort
> --makefile' and our local code tree via 'ghc -M'. In addition to the
> recompilation checker fixes of #5878, the following would be great to
> have in 7.4.2:
>
> 1) http://hackage.haskell.org/trac/ghc/ticket/5891 -- the patch fixes
> a race condition in creating parent directories for built object files

Due to be merged.

> 2) master commit b6f94b5 "Compile link .note section separately from
> main.c" -- I think this is the patch that fixes link errors we've seen
> during parallel builds (via ghc -M) with 7.4.1, such as:
>
> /x/y/z.o: file not recognized: File truncated
>
> and:
>
> /usr/bin/ld: BFD (GNU Binutils for Ubuntu) 2.20.51-system.20100908
> internal error, aborting at ../../bfd/merge.c line 872 in
> _bfd_merged_section_offset

I've asked Ian to merge this into the branch, so it will be in 7.4.2.

> Will everything currently in master already be included in the next
> release or is it a separate branch? (If it's a separate branch I'll do
> some more testing to confirm that b6f94b5 is the patch that fixes the
> link error).

The branch is separate (ghc-7.4) and we merge specific fixes from 
master.  The best way to make sure we don't forget something is to make 
a ticket for it, then it goes through the open->merge->fixed workflow.

Cheers,
	Simon